Looking at the charging preferences of the Steam Deck, which from my research wants 45W at 15v/3A, it looks like the larger model should work just fine. And with it being $15 USD / $18 CAD this could be an incredible bargain.
It’s so new though I can’t find any info on it being used with a Steam Deck. I’ll definitely be grabbing one to try, as it would be perfect for my USB hub that sits by the TV.
There is no limit to when it will charge, you can use a lower power charger to extend your runtime - I use my 9V 2A (18W) Pixel 4a charger all the time while playing. Anything higher than 25w will keep you playing indefinitely, as that’s pretty much the limit for what the deck can draw - 15W TDP and 10W for the screen, but obviously if you draw more than your charger can output eventually you will run out of battery.
But for quite a few lighter titles, 18W still gives you a few watts of net positive.